Cellular operators may nowadays offer a local IP (Internet protocol) connectivity within a certain area (local IP breakout) without roaming, with limited user mobility and IP session continuation being an alternative to the ordinary cellular packet data services with roaming and global mobility support. Such local IP connectivity may be provided within a local zone in a city center or any limited geographical area, an enterprise network or a home where radio coverage is available. In minimum, this kind of local IP breakout can be provided using one radio cell/base station and it may be expanded to a wide radio coverage area in the operator's nation wide domain (PLMN). For example, LTE/SAE (long term evolution/system architecture evolution) service with roaming, and global/Inter radio access mobility with IP session continuation may be overlapping and may share the same cells/base stations that provide the local IP breakout service.
The default user IP connectivity using a SAE gateway that provides global roaming and mobility support can be available in parallel with LBO (local breakout) services that use a Local IP GW (access router) in the local IP breakout service area. It would be desirable to provide session continuation for an ongoing LBO sessions while the user equipment (UE) happens to move out of the local IP breakout service area, e.g. user is leaving an office or a Home Base Station having an active VoIP call.
Network access to ordinary cellular packet data services is enabled e.g. in LTE/SAE via the cellular operator's core network that provides global roaming and mobility support. Normally UE (user equipment, mobile terminal) is connected to the radio network, such as E-UTRAN (enhanced universal terrestrial radio access network) in the LTE/SAE of this example, in a way that a SAE gateway that is located in the core network provides an IP point of attachment to the UE. The selection of this gateway takes place during an Initial Attach procedure when the UE is also authenticated and authorized to use the network services. The SAE gateway can be selected either from the visited PLMN (public mobile network) or the UE's home PLMN, depending on the roaming agreement between the operators. If a SAE gateway is selected from the visited PLMN, a “local breakout” with roaming is in question.
When the UE moves out of the local IP breakout service area, the user traffic using the current IP address for the LBO services is no more routable to the UE in the access network as the new base station may be located in an incorrect IP subnet in the IP network topology at the transport layer. Normally such a situation would mean breaking the active LBO session because the current IP address would no more be routable to reach the UE. A mobile IP could provide IP session continuation out of the LBO service area but that would require using a home agent (HA) service, i.e. an external access router higher in the IP network topology providing the actual user IP point of attachment. Thus, the mobile IP follows the idea of a single switch providing only “long distance calls” like it is with using the centralized SAE GW in the standard LTE/SAE architecture. One of the main ideas in the local IP breakout is, however, to provide optimized local routing, i.e. local calls in a cellular network.
Even if it is assumed that the SAE bearer services will be available in parallel, it is not possible to switch in the UE to use the IP address/APN for the SAE bearer services as this address is different than the IP address for the LBO services. Changing an IP address during a session would automatically break the LBO service (no means to indicate to the corresponding node(s) about the changed IP address).
Several home base station (Femto base station, home eNB, HNB etc.) vendors have proposed an architecture where eNB/(MME)/SAE GW functions are integrated to a Femto (i.e. home) base station in order to get local breakout directly from the Femto base station to e.g. Internet. The drawback of this solution is that the IP session cannot be maintained if the UE moves out of the Femto cell coverage. When the UE moves to a macro cell, it needs to use a SAE bearer from a SAE GW located in the operator's network.
In a known contribution of 3GPP TSG-RAN WG3 R3-070977, Kobe, Japan, 7-11 May 2007: “Requirement discussion for Home ENB”, a requirement for a direct communication between two UEs in the same home base station (H-NB) without a CN (core network) user plane intervention is proposed. The same contribution also proposes a requirement for UE movement from an H-NB to a macro cell without service downgrade compared to ordinary Inter-eNB handover. However, in the second contribution (R3-070978), the mobility scenario for LTE HNB→LTE MACRO is described only in LTE Idle mode. However, there cannot be found any solutions for session continuation in LTE active mode while the UE moves out of the H-NB coverage area.